By controlling the majority of the network's computing power, hackers can alter the blockchain and reverse transactions that they have made, effectively allowing them to spend the cryptocurrency twice.

Ethereum Classic, one of the most popular forks of the second most valuable cryptocurrencies by marketcap has suffered a 51-percent attack. After Chinese blockchain security firm SlowMist raised the alarm, an analyst at CoinNess dug a little deeper. The analyst found that a private mining pool had managed to increase its hash power to 3,263 GH/s, making it – temporarily – the most powerful mining pool at around 11:00am UTC on 6 January. After this brief spike in power, the mining pool returned...